Dialysis is performed as a treatment for patients suffering from renal insufficiency. Dialysis can be performed either in the peritoneum, or through extracorporeal dialysis involving filtration of blood. These two dialysis methods have in common the fact that dialysis fluids or dialysates take up the degradation products of metabolism. These dialysates usually contain high levels of sodium chloride and other electrolytes, such as calcium chloride, or potassium chloride, a buffer substance, such as bicarbonate, or acetate and acid to establish a physiological pH, plus optionally, glucose or another osmotic agent.
Dialysates are either supplied as ready-to-use solutions or they are prepared on site from concentrates, including solid concentrates. Solids offer the advantage of a small package volume and a low weight. Although solids also have disadvantages—electrolyte salts, for example, are highly hygroscopic—there is a trend toward offering only solid components for preparation of dialysates.
In the above mentioned hemodialysis systems, a flexible bag or container filled with a powdered salt concentrate is used to generate a concentrated salt solution. Purified fluid is added to the top of the container and the concentrated solution is removed from the bottom of the container. When the concentrated solution is removed from the bottom of the bag it is generally delivered to the hemodialysis machine for use in the dialysate. It is important that the fluid level in the container with the salt concentrate is maintained above the level of the salt in the container, when the solution is being pumped out of the bottom of the container. Under normal operation, the fluid level above the powdered salt layer is maintained or increases as the salt concentrate is consumed. However, if the fluid level falls below the level of the salt concentrate, air or gases in the bag may be pumped through the salt concentrate and out of the bottom of the container into the dialysate.
During hemodialysis using systems such as described in U.S. Pat. No. 5,385,564 and U.S. Pat. No. 5,616,305, incorporated by reference herein, dry bicarbonate or acid concentrate is mixed with dialysate via a container using one or more ports. Even when the container is filled there is always air remaining in the container. The system cannot remove all of the air from the container without evacuating the air from the container via a vacuum system to create negative pressure, before filling the container with fluid.
To deter air from being drawn into the hydraulics of the machine during operation, it is desirable to fill the container with a sufficient volume or fluid to maintain a fluid layer above the dry powder. In some systems, without removing air from the bag via a vacuum, some containers will not maintain the correct fluid layer, and thus, extra air passes into the hydraulics which requires excessive venting procedures. The new method and arrangement of the present invention addresses the problem without the need to generate a vacuum to evacuate the gases from the concentrate.